1. Field of the Invention
This invention relates to novel chemical compositions for golf ball covers, construction and manufacturing processes that provide improved manufacturability and playability characteristics.
2. Description of the Related Art
Until the late 1960's, most golf balls were constructed with a thread wound core and a cover of compounds based on natural (balata and gutta percha) or synthetic transpolyisoprene. These golf balls have been and are still known to provide good flight distance. Additionally, due to the relative softness of the balata cover, skilled golfers can impart various spins on the ball in order to control the ball's flight path (e.g., “fade” or “draw”) and “bite” characteristics upon landing on a green. “Fade” is the term used in golf to describe a particular golf ball flight path that is characterized by a curved or arched flight exhibited towards the latter portion of the flight path that veers off from the center line of the initial flight path to the right of a right-handed golfer. Upon contact with the ground, a ball hit with “fade” will stop in a relatively short distance. “Fade” results from imparting clockwise sidespin on the golf ball.
“Draw” is the term used in golf to describe a particular golf ball flight path that is characterized by a curved or arched flight exhibited towards the latter portion of the flight path that veers off from the center line of the initial flight path to the left of a right-handed golfer. Upon contact with the ground, a ball hit with “draw”, unlike a ball hit with “fade”, will roll for a considerable distance until coming to rest. “Draw” results from imparting counter-clockwise sidespin on the golf ball.
“Bite” is the term used in golf to describe the effect of imparting a substantial amount of backspin to an approach shot to a green which causes the golf ball to stop abruptly upon contact with the green.
Another desirable feature of balata-based compounds is that they are readily adaptable to molding. These compounds therefor can be easily compression molded about a spherical core to produce golf balls.
Though possessing many desirable properties, there are substantial drawbacks to use of balata or transpolyisoprene-based compounds for golf ball covers. From a manufacturing standpoint, balata-type materials are expensive and the manufacturing procedures used are time consuming and labor-intensive, thereby adding to the material expense. From a player's perspective, golf balls constructed with balata-based covers are very susceptible to being cut from mishits and being sheared from “sharp” grooves on a club face. As a result, they have a relatively short life span.
In response to these drawbacks to balata-based golf ball covers, the golf ball manufacturing industry has shifted to the use of synthetic thermoplastic materials, most notably ionomers sold by E. I. DuPont De Nemours & Company under the name SURLYN.
Thread wound balls with ionomer covers are less costly to manufacture than balls with balata covers. They are more durable and produce satisfactory flight distance. However, these materials are relatively hard compared to balata and thus lack the “click” and “feel” of a balata covered golf ball. “Click” is the sound emitted from the impact of a golf club head on a golf ball. “Feel” is the overall sensation transmitted to the golfer through the golf club after striking a golf ball.
In an attempt to overcome the negative factors of the hard ionomer covers, DuPont introduced low modulus SURLYN ionomers in the early 1980's. These SURLYN ionomers have a flexural modulus from about 3000 to about 7000 PSI and peak hardness from about 25 to about 40 as measured on the Shore D scale-ASTM 2240. The low modulus ionomers are terpolymers, typically of ethylene, methacrylic acid and n- or iso-butylacrylate, neutralized with sodium, zinc, magnesium or lithium cations. E.I. DuPont De Nemours & Company has disclosed that the low modulus ionomers can be blended with other grades of previously commercialized ionomers of high flexural modulus from about 30,000 to 55,000 PSI to produce balata-like properties. However, “soft” blends, typically 52 Shore D and lower (balata-like hardness), are still prone to cut and shear damage.
The low modulus ionomers when used without blends, produce covers with very similar physical properties to those of balata, including poor cut and shear resistance. Worse, wound balls with these covers tend to go “out-of-round” quicker than wound balls with balata covers. Blending with hard SURLYN ionomers was found to improve these properties.
Another approach taken to provide a golf ball cover that has the playing characteristics of balata is described in U.S. Pat. No. 5,334,673 (“the '673 patent”) assigned to the Acushnet Company. The '673 patent discloses a cover composition comprising a diisocyanate, a polyol and a slow-reacting polyamine curing agent. The diisocyanates claimed in the '673 patent are relatively fast reacting. Due to this fact, catalysts are not needed to lower the activation energy threshold. However, since relatively slow-reacting curative systems are used, a catalyst is added to speed the reaction. Because a catalyst is used, the reaction rate cannot be easily controlled thereby requiring the implementation of substantial processing controls and precise reactant concentrations in order to obtain a desired product.
Isaac (U.S. Pat. No. 3,989,568) does not disclose toluene diisocyanate, 4,4′-diphenylmethane diisocyanate, Isophorone diisocyanate or their mixtures. He teaches a step-wise process for making polyurethane-based golf ball covers. The process involves the steps of making sheets, cutting the sheets into square preforms, molding half-shells, compression molding golf balls along with a post-cure or extended compression molding cycle. The Isaac process requires the addition of a catalyst to the polymer system.
The Isaac process cannot be used with the components of the presently disclosed polyurethane system. The compression molding taught by Isaac is damaging to the core of a golf ball that is made with thread windings. According to the Isaac process, the compression molding takes place at 240° F. for 5 minutes or, to eliminate the post-cure, for 10-12 minutes. Under either conditions, the performance characteristics of the thread wound core of the golf ball would be unacceptably compromised. In contrast, a golf ball made in accordance with the components and processing steps of the instant invention would experience a temperature of less than 160° F. for only about 5 minutes.
Furthermore, the post-cure of Isaac requires preferably two months at room temperature for completion. Two months work-in-process is impractical. The presently disclosed process overcomes this problem by a novel combination of components and processing steps that requires only an 8 hour room-temperature post-cure which amounts to 0.56% of the time required by Isaac. Apart from this difference, the present invention's claimed components and process eliminate many of the steps of Isaac such as the post-cure requirement.
The Isaac process is further incompatible with the presently claimed chemistry and process since with the presently claimed chemistry and process, a thermoset polymer is produced from a liquid mixture in less than one minute. The resulting thermoset polymer cannot be re-formed under heat or pressure. Neither Wu nor Presswood (U.S. Pat. No. 4,631,298) provide teachings to overcome this problem and, in fact, teach away from being combined with Isaac to obviate the presently claimed invention.
Wu discloses prepolymer compositions based on diisocyanates and polytetramethylene ether glycol with a slow reacting curing agent and method of producing golf ball covers. Presswood discloses the use of fast and slow reacting polyamines to cure polyurethane polymers. The two references teach away from each other as well as Isaac for the following reasons.
The chemistry disclosed by Wu, which involves a prepolymer, a slow reacting diamine and a catalyst caters to a method involving several manufacturing steps. This method includes several curing steps requiring a combined 66-94 minutes and the use of a catalyst, which makes the process very difficult to control. Wu is further limited to a multi-stage molding process as described in columns 5 and 6. The presently disclosed composition could not be used in a process as described by Wu nor could the chemistry of Wu be used in the presently disclosed process. The amount of catalyst that is required to use the chemistry of Wu in The presently disclosed process would make the reaction uncontrollable and thus unsuitable for manufacturing purposes. The relatively rapid cure of The presently disclosed composition would be unsuitable in the multi-stage process of Wu. In short, the chemistry and process of Wu is incompatible with The presently disclosed chemistry and process. As such, Wu teaches away from The presently disclosed claimed composition and chemistry even in view of Isaac and Presswood.
Although Presswood discloses a curing agent blend, it is taught as being used in a reaction injection molding (RIM) process that has novelty due to the high green strength resulting in fast RIM cycle times. A golf ball cover molded by a RIM process is not feasible using current engineering practices. Locating a spherical wound core in a spherical molded cover cannot be accomplished in one step as suggested by the teachings of Wu, Isaac, Ward (U.S. Pat. No. 3,147,324, discussed below) or Watson (U.S. Pat. No. 3,130,102, discussed below).
The chemistry and process of The presently disclosed claimed invention is not compatible with a RIM process. First, the speed of a RIM process, even with the use of slow reacting curing agents, is far too fast to accomplish the task of placing a core in the curing polymer. Because of the rapid speed of the reaction, even if the cover were poured in hemispherical segments, by the time the second hemisphere was poured, there would not be enough reactivity left in the second poured half to bond to the first poured half. The reaction time is simply too quick for current production methods.
Second, it would not be possible to suspend a core within the center of a mold using the RIM process. The uneven surface of a wound core would not allow for adequate centering and would produce an inferior golf ball. Additionally, the use of pins to suspend a core in the approximate center of a mold would cause additional problems when the thermoset composition of The presently disclosed claimed composition would adhere to the pins and thus make it impractical. Again, from a manufacturing perspective, the teachings of Presswood are not compatible with The presently disclosed claimed chemistry or process.
A further problem with the teachings of Presswood is the resulting high green strength of the polymer. The presently disclosed claimed composition and process produce a polymer with low green strength which does not allow for quick removal from the molds being used. The presently disclosed composition is only compatible with a cast process.
Accordingly, Presswood does not teach or motivate one skilled in the art when viewed with the process of Isaac and the chemical component teachings of Wu to provide a catalyst-free polyurethane system that eliminates a number of processing steps including long post-cure periods to provide a polyurethane-covered golf ball exhibiting superior playability characteristics.
The presently disclosed process as claimed, is designed to be relatively fast and continuous. These characteristics of the presently disclosed process are dictated by the novel chemistry as claimed. The process in Ward differs markedly from the presently disclosed process in that the presently disclosed process produces a thermoset polymer from a liquid mixture in less than one minute. The presently disclosed claimed composition cannot be reformed under heat or pressure. The teachings of Ward's process retards the curing process. Ward's process is incompatible and does not render obvious the presently disclosed process since use of Ward's process with the presently disclosed composition would result in the initial cure of the first mold half containing the golf ball core being complete before the second mold half is filled with urethane mixture. Our invention requires that the second mold half to be filled after the first mold half and before the core is loaded into the first mold half. Ward does not teach this sequence. Neither Isaac nor Watson teach this sequence.
Watson specifically teaches the manufacture of golf balls from half-shells that have been frozen to halt the curing process. These steps are inherently slow and expensive and thus undesirable. The presently disclosed process eliminates the need to halt the curing process and in fact teaches a way of streamlining and maximizing the speed of the process without compromising the superior characteristics of the final product.
Isaac also teaches the interruption of the processing cycle by describing how to partially cure the polyurethane which allows the half-shells to be produced and handled and then compression molded to form dimples and the cover around the core. The presently disclosed claimed process eliminates the delays caused by the process of Isaac. The presently disclosed composition also does not allow the use of the process teachings of Isaac. Watson and Isaac teach how to arrest the curing process. The presently disclosed claimed process teaches how to streamline and speed the process.
To avoid the problems associated with fast-reacting prepolymer systems, slow-reacting systems such as Toluene diisocyanate (TDI) prepolymer systems can be employed. However, these systems, while avoiding the problems associated with fast-reacting systems, present similar problems, albeit for different reasons. The most noteworthy problem with slow-reacting pre-polymer systems is the requirement for a catalyst.
By introducing a catalyst into the system, processing problems similar to those associated with fast-reacting pre-polymer systems are virtually inevitable. As is well known in the art, the use of a catalyst can severely restrict the ability to control the speed of the reaction, which is undesirable.
It has now been discovered that a blend of diamine curing agents with slow-reacting prepolymer systems eliminates the problems associated with catalysts while maintaining the advantages associated with slow-reacting prepolymer systems. Accordingly, it is an object of the present invention to provide a golf ball cover composition that does not require a catalyst.
It is another object of the present invention to provide a golf ball having a synthetic cover material that achieves the click, feel, playability and flight performance qualities of balata covered golf balls.
It is yet another object of the invention to provide a polyurethane formula that achieves hardness characteristics similar to those associated with balata without compromising the durability of the polyurethane material. In contrast, polyurethane systems such as those disclosed in the '673 patent produce relatively high hardness ranges that obviate the possibility of providing a polyurethane system that can truly mimic the feel and playability of a balata-based product.
It is yet another object of the invention to put a urethane cover on a golf ball core in a single manufacturing step.
It is yet another object of the invention to provide a polyurethane formula that eliminates the damaging high temperature post cure operation.
A further object of the present invention is to provide a golf ball cover material that has improved manufacturing process as well as improved durability and resilience over balata.